Method for controlling an electro-surgical hf generator and electro-surgical device

ABSTRACT

In an electro-surgical high-frequency generator, the signal frequency or the modulation frequency or a clock frequency or any combination thereof are modulated using a low-frequency modulation signal in such a way that the spectra thereof are widened. This results in a reduction of interference on peripheral devices.

The invention relates to a method for controlling an electro-surgical HFgenerator and an electro-surgical device according to the preamble toclaim 1 or claim 7.

Modern surgery frequently makes use of electro-surgical devicesincluding a high-frequency generator for generating a high-frequencyalternating current. This high-frequency alternating current is thenused to cut or coagulate biological tissue or treat it in some otherway.

The fundamental frequency of the HF generator is usually between 300 kHzand 4 MHz. Depending upon the application, this high-frequency ismodulated in different ways with respect to its amplitudes. Usually,pulse duration modulation is performed in order to determine the powerapplied. Here, the ratio of burst-type signal segments to succeedingpauses is set. The clock frequency or modulation is usually performedwith frequencies of between 1 kHz and 50 kHz.

In addition, further modulation (switching the output signal on and off)is performed with very low frequencies between 1 Hz and 10 Hz to achievea power intensity which enables the operator to follow the progress ofthe treatment.

Finally, to avoid leakage currents or losses from the generators duringidling with no load, very low-frequency pulses, ie sine beats of thefundamental frequency are used.

In addition to electro-surgical devices, nowadays, a plurality of otherelectrical or electronic devices is used in the operating theatre. Theseare in particular patient monitoring devices (for example EEG devices)or video devices. A typical example of a video device essential for anoperation is used in operations performed using endoscopy. In this case,the video chip is located in the immediate vicinity of the location atwhich an electro-surgical instrument is used to apply theabove-described high-frequency alternating current to tissue.

In all the above cases, there is frequently interference with theelectronic device, which could even result in the failure of the patientmonitor used meaning that, after a certain time, it is not possible tomonitor the vital parameters of the patient. The same applies to thevideo picture. In all cases, problems of this kind can have fatalconsequences for the patient.

It is an object of the present invention, to disclose a method or anelectro-surgical device of the type named in the introduction with whichinterference, in particular on peripheral devices, is avoided or atleast reduced.

This object is achieved by a method according to claim 1 or anelectro-surgical device according to claim 7.

In particular, the object is achieved by a method for controlling anelectro-surgical HF generator, which generates a high-frequency outputsignal for treating, in particular for cutting or coagulating biologicaltissue, wherein the HF generator is embodied in such a way that theoutput signal has a predetermined signal frequency and is generatedcontinuously, modulated with a modulation frequency, or in bursts with apredetermined signal-to-pause pulse-duty ratio and a predetermined clockfrequency. Here, the signal frequency and/or the modulation frequencyand/or the clock frequency is modulated with a low-frequency modulationsignal so that the spectra of signal frequency or modulation frequencyor clock frequency are widened.

An essential point of invention is therefore the fact that, according tothe present invention, the modulation frequency or clock frequency, butalso the signal frequency, which was previously kept constant, are notkept at a constant value. With an observation in the frequency range,this results in a widening of the (generated by constant frequencies)spectral lines into spectral bands. This “frequency spread” results ingreatly reduced peak values of the power, since the energy generated isnot generated with one single frequency, but divided between a pluralityof frequencies or a frequency band. This in turn achieves a significantreduction in both conducted and wireless interfering emissions, whichhas a favourable influence on the important EMC limit values of thedevice. This in turn results in a direct reduction in the electricalinterference on patient monitors, video systems and other electrical orelectronic devices with all the problematic consequences described. Thisadditional modulation of the signals has no impact on the surgicaleffects, which are all very inert, since they are primarily based onthermal effects.

The modulation signal is preferably generated in a frequency rangeoutside those frequencies which cause interference in peripheral medicaldevices, in particular in patient monitoring systems or patientmonitoring or video systems. Here, despite the low signal energy, whichcontains the modulation frequency, as with the other modulationfrequencies, it is therefore ensured that the action of interferingradiation is kept as low as possible.

The modulation signal preferably has a substantially constant course sothat therefore no sudden frequency changes and hence further (higherfrequency) interference signals could occur.

The modulation signal can be embodied in a different ways. It can be apreferably constantly sweeping signal so that the fundamental frequencyand/or the clock frequency or the modulation frequency of the signal arechanged continuously.

Another possibility is to embody the modulation signal as a random ornoise signal.

It is also of advantage for the modulation signal to be set in afrequency range at or close to the system frequency. At this frequency,to be precise, the electronic devices used are usually equipped witheffective blocking filters so that interference signals are suppressedin this range without any additional measures by filters that would beprovided in any case.

With respect to the device, the above object is achieved by aelectro-surgical device with a high-frequency generator, which generatesa high-frequency output signal for treating, in particular for cuttingor coagulating, biological tissue, wherein the high-frequency generatoris embodied in such a way that the output signal has a predeterminedsignal frequency and is generated continuously, modulated with amodulation frequency, or in bursts with a predetermined signal-to-pausepulse-duty ratio and a predetermined clock frequency. Here, a modulationgenerator is provided, which generates a low-frequency modulationsignal, which is supplied to the HF generator for controlling the outputsignal in such a way that the signal frequency and/or the modulationfrequency and/or the clock frequency with the low-frequency modulationsignal are modulated so that the spectra thereof are widened.

The advantageous embodiments of the invention have already beenexplained with reference to the method described in the introduction andobviously also apply to the electro-surgical device claimed here.

The following describes an exemplary embodiment of the invention withreference to diagrams, which show

FIG. 1 a block diagram of an embodiment of the electro-surgical deviceaccording to the invention and

FIG. 2-4 different signal shapes with the associated spectra.

In the following description, the same reference numerals denote thesame parts or parts having similar functions.

FIG. 1 is a greatly schematised drawing of an embodiment of anelectro-surgical device according to the present invention. Details ofthis type of known electro-surgical device may be found for example inDE 199 43 792 C2, DE 100 46 592 C2, EP 0 430 929 B1 or EP 0 653 192 B1,to which express referral is made here.

An electro-surgical device of this kind comprises a high-frequencygenerator 10, which encompasses an oscillator 11, the output signal ofwhich with the frequency f₀ is switched via a switch 12 and amplified byan output amplifier 13 so that an output signal U_(out) is present atthe output of the HF generator 10. Here, it is stressed here that thisis a schematic representation to explain the mode of operation of thearrangement.

To adjust the output amplitude U_(peak), an adjusting device 14 isprovided, which adjusts the amplification factor of the output amplifier13. To control the switch 12, a switch control 16 is provided whichadjusts the pulse-duty ratio via an adjusting device 15, that is theduration t_(on), for which the output signal of the oscillator 11 ispresent at the input to the output amplifier 13, divided by the timet_(off) during which the switch 12 is on.

The oscillator 11 is shown in the present example as VCO, that is anoscillator, the oscillation frequency f_(HF) of which can be controlledby a voltage. This voltage is selected by a modulation generator 20.

The switch control 16 has a second input, via which a signalt_(on)+t_(off) is received and processed so that the switch 12 iscontrolled with the predetermined pulse-duty ratio t_(on)/t_(off) forthe period t_(on)+t_(off). This “period signal” represents a modulationsignal, which is generated by a modulation generator 20′.

The following describes the mode of operation of this schematicallydepicted embodiment of the invention.

FIG. 2 shows the temporal course of a high-frequency signal with thefrequency f₀ modulated by the switch 12 with a period T=t_(on)+t_(off).The representation shown in FIG. 2 b is a frequency spectrum in whichthe power P of the signal can be seen from the frequency. Theconventionally modulated high-frequency signal shown in FIG. 2 aresults, on the one hand, in a sharp spectral line, which is designatedIII in FIG. 2 b. The modulation period T results in a spectral line,which is designated II in FIG. 2 b.

FIG. 2 b also shows another spectral line I, which is in the verylow-frequency range and originates from the signal modulation describedin the introduction, which is performed during “inactive” periods of usein order to keep the losses low.

FIG. 2 c shows a signal, which, according to the present invention, has,on the one hand, a constant modulation period T, but with which, on theother hand, the high-frequency signal is not present with a constantfrequency f₀, but is swept. Therefore, the frequency rises over time andwith each new period starts again at the lower frequency. This sweptsignal according to FIG. 2 c results in the spectrum shown in FIG. 2 baround the spectral line III, since lower frequency components andhigher frequency components are present. However, when the modulationfrequency for switching on and off of the signal is unchanged comparedto FIG. 2 a, the spectral line II in FIG. 2 b is retained.

FIG. 3 a shows a signal, with which the frequency f₀ of thehigh-frequency signal is unchanged. In addition, the signal according toFIG. 3 a has a constant pulse-duty ratio t_(on)/t_(off)=2/1, wherein theperiods T of individual signals consisting of a burst and a followingpause vary in time. This results in a spectrum, as shown in FIG. 3 b, inwhich the lower frequency, resulting from period T appears as aspectrum, while the high-frequency signal generates a sharp spectralline.

FIG. 4 a now shows bursts, with which the pulse-duty ratio is alwayst_(on)/t_(off)=2.5/1. The high-frequency signals within these burstshave a varying frequency. In addition, the periods T are different.

The signal course according to FIG. 4 b differs from that in FIG. 4 a inthat the periods T do not rise continuously, but vary randomly.Otherwise, with the signal according to FIG. 4 b, the pulse-duty ratiois again always 2.5/1.

These two signals shown in FIGS. 4 a and 4 b now result in a spectrum asshown in FIG. 4 c. Here, it is evident that the sharp spectral linescorresponding to the high-frequency signal or the modulations-clockfrequency have disappeared and are replaced by broad spectra.

A comparison of the signal originating from a conventionalelectro-surgical generator according to FIG. 2 a and the resultingspectrum according to FIG. 2 b or 3 c now reveals that the maximumpowers of sharp spectral lines, such as those obtained from continuoushigh-frequency signals or modulation with a constant frequency, fallsignificantly on the variation of the signal frequency or modulationfrequency. This achieves the desired objective of greatly reducing theinterfering radiation or the system-induced interference componentswhich could have detrimental impacts on peripheral devices. Here, it issufficient if the mean value of the frequencies of the HF signal or themodulation frequency only fluctuates by a few percent in order toachieve the described frequency spread, that is the expansion ofindividual spectral lines, into a widened spectrum.

This control of the signal or modulation frequency can be performed bythe modulation generators 20 and 20′ either regularly, for example witha sinusoidal signal or with any other type, in particular with a noisesignal. If the modulation is performed with a sinusoidal signal, a newspectral line (not shown in the diagrams) appears again in the outputspectrum. If this spectral line is set so that it lies within a rangethat causes little interference to peripheral devices, for example atthe system frequency, only low interference on the peripheral devices isto be expected since any interference to them is already usuallysuppressed in this frequency range. If the modulation generators 20, 20′modulate stochastically, once again an “interference spectrum” isgenerated, but, due to the above-described widening, its amplitude isvery low. Here, once again, the centre frequency of the noise signal canadvantageously be set in a range in which the peripheral devices to beprotected from interference are “insensitive”.

It may be derived from the above that an essential principle of theinvention lies in the fact that periodic processes, that is the actualhigh-frequency signal and all modulation processes, which are used togenerate special effects, are not kept constant but varied in time inorder to avoid sharp spectral lines with high powers.

LIST OF REFERENCE NUMBERS

-   -   10 HF generator    -   11 Oscillator    -   12 Switch    -   13 Output amplifier    -   14 Amplitude adjusting device    -   15 Pulse-duty-ratio adjusting device    -   16 Switch control    -   20, 20′ Modulation generator

1. A method for controlling an electro-surgical high-frequency.generator whose output is for treating biological tissue by cutting orcoagulating, said method comprising: using the high-frequency generatorto generate a high-frequency output signal having a predetermined signalfrequency, the output signal either being generated continuously andmodulated with a modulation frequency or being generated in bursts andhaving a predetermined signal-to-pause pulse-duty ratio and apredetermined clock frequency; and modulating the signal frequency orthe modulation frequency or the clock frequency or any combinationthereof with a low-frequency modulation signal so that the spectrathereof are widened.
 2. The method according to claim 1, furthercomprising generating the low-frequency modulation signal in a frequencyrange outside that of those frequencies which cause interference inperipheral medical devices.
 3. The method according to claim 2, whereinthe low-frequency modulation signal has a substantially constant course.4. The method according to claim 2, wherein the low-frequency modulationsignal is a random or noise signal.
 5. The method according to claim 2,wherein the low-frequency modulation signal is a constantly sweepingsignal.
 6. The method according to claim 2, wherein the modulatingresults in the signal frequency or the modulation frequency or the clockfrequency or any combination thereof being varied less than 20%.
 7. Aelectro-surgical device comprising: a high-frequency generator whichgenerates a high-frequency output signal for treating biological tissueby cutting or coagulating, wherein the high-frequency generator isconfigured to output the output signal with a predetermined signalfrequency and to generate the output signal continuously, modulated witha modulation frequency, or in bursts with a predetermined pulse-dutyratio of signal-to-pause and a predetermined clock frequency; and amodulation generator which generates a low-frequency modulation signalwhich is fed to the high-frequency generator for controlling the outputsignal so that the signal frequency or the modulation frequency or theclock frequency or combinations thereof are modulated with thelow-frequency modulation signal so that the spectra thereof are widened.8. The electro-surgical device according to claim 7, wherein themodulation signal is generated in a frequency range outside that ofthose frequencies which cause interference in peripheral medicaldevices.
 9. The electro-surgical device according to claim 8, whereinthe modulation signal has a substantially constant course.
 10. Theelectro-surgical device according to claim 8, wherein the modulationsignal is a random or noise signal.
 11. The electro-surgical deviceaccording to claim 8, wherein the modulation signal is a constantlysweeping signal.
 12. The electro-surgical device according to claim 8,wherein the signal frequency or the modulation frequency or the clockfrequency or any combination thereof are varied by less than 20%. 13.The electro-surgical device according to claim 12, wherein the signalfrequency or the modulation frequency or the clock frequency or anycombination thereof are varied by less than 10%.
 14. Theelectro-surgical device according to claim 13, wherein the signalfrequency or the modulation frequency or the clock frequency or anycombination thereof are varied by less than 5%.
 15. The electro-surgicaldevice according to claim 8, wherein the peripheral medical deviceswhich are not subject to interference by the modulation signal includepatient monitoring systems and video systems.
 16. The method accordingto claim 2, wherein the peripheral medical devices which are not subjectto interference by the modulation signal include patient monitoringsystems and video systems.
 17. The method according to claim 6, whereinthe modulating results in the signal frequency or the modulationfrequency or the clock frequency or any combination thereof being variedless than 10%.
 18. The method according to claim 17, wherein themodulating results in the signal frequency or the modulation frequencyor the clock frequency or any combination thereof being varied less than5%.